Fluorite, barite and calcite are important industry minerals. However, they often co-exist, presenting difficulty in selectively separating them due to their similar surface properties. In this study, valonea extract and sodium fluosilicate were used as depressants to selectively separate them by flotation, with sodium oleate as the collector. The single mineral flotation results showed that valonea extract displayed the strongest depression on calcite, while sodium fluosilicate displayed the strongest depression on barite. These two depressants allowed selective separation of the three minerals through sequential flotation. The flotation of mixed minerals showed that 94% of the calcite was successfully depressed by the valonea extract, and 95% recovery of the fluorite was achieved in the subsequent flotation with sodium fluosilicate depressing barite. The different depressant–mineral interactions were investigated via electro-kinetic studies and molecular dynamics (MD) simulations using the Materials Studio 6.0 program. The valonea extract exhibited the strongest adsorption on the calcite surface, and sodium fluosilicate exhibited the strongest adsorption on the barite surface, which prevented oleate species from reacting with Ca²⁺ or Ba²⁺ surface sites. This study provides useful guidance for how to process fluorite, barite and calcite resources.

Kyanite and sillimanite are two polymorphic minerals with the same formula of Al₂SiO₅, but different crystal structures. Despite their high economic values, selectively recovering them by flotation is a challenge. In this study, the flotation behaviors of the two minerals with sodium oleate as the collector were examined at different pH conditions. Zeta potential measurement, infrared spectroscopic measurement, chemical speciation and X-ray photoelectron spectroscopy measurement were conducted to identify the underpinning mechanisms. It is found that the flotation behavior of both minerals is different under the same flotation condition. The flotation recovery of sillimanite is much higher than that of kyanite in the presence of the collector sodium oleate. Sodium oleate adsorbs onto the surfaces of kyanite and sillimanite mainly through the chemical interaction of the ionic–molecular dimers with aluminum atoms at pH 8.0. The higher sillimanite flotation recovery between the two minerals is related to the higher electrostatic charge densities of the aluminum atoms in six-fold coordination, which leads to the higher collector adsorption.

The effects of Ca2+ ions on the flotation of sillimanite using dodecylammonium chloride as a collector were investigated by micro-flotation tests, zeta potential measurements, solution chemistry analysis and molecular dynamics (MD) simulation. The micro-flotation results indicated that Ca2+ ions remarkably inhibit the flotation of sillimanite in the pH range of 2.0–9.0. The point of zero charge (PZC) of sillimanite changed from 5.4 to 6.1 with the addition of Ca2+ ions. Meanwhile, the calculated concentration of RNH3+ in the sillimanite interface layer decreased in the presence of Ca2+ ions. The results of MD simulation revealed that Ca2+ ions have strong binding energy with the sillimanite (010) surface, and the binding energy of RNH3+ with sillimanite (010) surface reduced in the presence of Ca2+ ions. The conclusions drawn from the computations are in good agreement with the experimental results.